Smoke detector failure alarm

ABSTRACT

In a smoke detector a regulated, half-wave rectifier supplies power for an exciter lamp, a photocell shielded from the lamp but viewing an area illuminated by the lamp, and a relay switching circuit triggered by the cell for applying the half-wave current to the winding of a horn so as to cause the horn to sound at the half-wave frequency when the cell senses smoke scattered from the illuminated area. The switching circuit for the horn can also be triggered by a thermostatic switch responsive to high ambient temperature. Failure of the exciter lamp or voltage regulator deenergizes the relay, switching in a pulsing circuit which sounds the horn at a distinctively different frequency than the smoke alarm.

United States Patent [191 Enemark [111 3,774,186 Nov. 20, 1973 SMOKE DETECTOR FAILURE ALARM [75] Inventor: Robert B. Enemark, Weymouth,

Mass.

[73] Assignee: Electro Signal Lab. Inc., Weymouth,

Mass,

[22] Filed: Mar. 15, 1972 [21] Appl. No.: 234,775

[52] US. Cl. 340/237 S, 340/384 E, 340/409 [51] Int. Cl. G08b 19/00 [58] Field of Search 340/237 S, 384 E, 340/409 [56] 7 References Cited UNITED STATES PATENTS 3,555,532. l/1971 White et a1. 340/237 S 3,446,649 9/1 969 Colman 340/384 E 3,487,404 12/1969 Midkiff 340/384 E X 3,693,110 9/1972 Briggs, Jr. et al. 340/384 E X Primary Examiner-John W. Caldwell Assistant Examiner-Daniel Myer Attorney-James H. Grover 57 ABSTRACT In a smoke detector a regulated, half-wave rectifier supplies power for an exciter lamp, a photocell shielded from the lamp but viewing an area illuminated by the lamp, and a relay switching circuit triggered by the cell for applying the half-wave current to the winding of a horn so as to cause the horn to sound at the half-wave frequency when the cell senses smoke scattered from the illuminated area. The switching circuit for the horn can also be triggered by a thermostatic switch responsive to high ambient temperature. Failure of the exciter lamp or voltage regulator deenergizes the relay, switching in a pulsing circuit which sounds the horn at a distinctively different frequency than the smoke alarm.

14 Claims, 2 Drawing Figures BACKGROUND Smoke detectors of the general type described in the abstract have utilized a relay circuit to actuate an auxilcell PC] is shielded from the lamp but views the illumialarm while still providing a distinctive indication of failure or inoperativeness of a smoke detector or other instrument for sensing physical conditions or changes.

SUMMARY OF THE lNVENTlON According to the invention an instrument of the type described comprises an electrical alarm instrument for sensing aphysical condition comprising, an electrical alarm, a controlled switch in series with the alarm and having a control, a power supply connected to the alarm and switch, a condition responsive circuit connected to the switch control to close the switch and actuate the alarm in a mode dependent on the power supply, and pulsing means connected to the switch control for pulse storage and discharge to the switch control thereby to close the switch and actuate the alarm in a different mode dependent on the pulsing means, the responsive circuit including switching means responsive to failure in said circuit to render the pulsing means effective, whereby the alarm indicates light response and circuit failure differently.

DRAWING For the purpose of illustration typical smoke detector circuits are shown schematically in FIGS. 1 and 2 of the accompanying drawing.

DESCRIPTION The smoke detector circuit shown operates on 120 volt alternating current supplied to terminals A and C. Through an ON-OFF switch S! the alternating current is connected to a pair of arc suppressor diodes D3 (EDAL l 6SP5B5) with a peak to peak breakdown voltage of about 300 volts which shunt high voltage transients through a current limiting resistor R1 (4.7 ohms). The transient-filtered current is half-wave rectified by a diode D 1 (1N4005). The half-wave voltage excursion at the positive terminal of the diode D1 is limited by a transistor Q1 (Motorola MJ-400) whose base voltage is held at the approximately 105 volts breakdown point of a zener diode D2 in series with a voltage dividing resistor R2 between the positive halfwave supply and a ground bus G. This regulated positive half-wave voltage is supplied through an exciter lamp DSl (Sylvania 60PSB) and a relay coil K in series, and also through a resistor R3 (33kilohms) to a pair of photocells PCI and PC2 (Clairex 5M7) in series with a resistor R6 (47 Kilohms). A reverse-connected diode D4 (1N4005) parallels the relay coil, and a by-pass capacitor C2 (0.001 microfarad) parallels the second photocell PCZ.

As is well known in the smoke detector art the exciter lamp DSl illuminates an area, usually within a dark chamber through which air circulates. The first photonated chamber. Light from the illuminated area is scattered back to the photocell PC! only when smoke or like air. born particles enter the illuminated area. The resistance and voltage drop across the first photocell PCl then falls from a high to a low value. The second photocell PCZ is normally at a constant low light level, and hence its resistance is constant except for aging effects with constant light source. When the first photo cell resistance drops, the voltage at the junction J of the two cells rises. When it rises to the firing threshold of a neon glow discharge lamp Ne l, at about 65 volts peak, the lamp abruptly conducts, applying a voltage to the gate 3 ofa silicon controlled rectifier switch (SCR) Q2 (GEC106B2). With the ON-OFF switch S1 in the closed position shown, the relay K is energized and its contact K1 is in the solid line position shown, so that the only path from the positive half wave supply through the coil L of an alarm horn H is through the SCR switch Q2. This switching device is normally open with its gate g near ground voltage. But the firing of the glow lamp Ne 1 causes the SCR to conduct and close the path through the horn coil L. The horn l-l then sounds at the half wave frequency supplied by the diode D1. While the SCR switch tends to cut off, i.e., open, during the nonrectified half cycle, the inductance L of the horn H produces a reactive current surge maintaining the SCR closed. The thermostatic switch TH, when closed by rise of ambient temperature, to say F, similarly raises the voltage at the SCR gate g sufficiently to close the SCR switch.

According to the present invention, when the relay coil K is de-energized by failure of'the voltage regulator transistor 01 or the exciter lamp US], the relay contact K1 is transferred to the broken line position Kl In this position a diode D5 (lN4005) is connected to shunt the reactive surges of the horn coil L, and a pulsing network is connected through the coil to the positive supply.

The pulsing network comprises a storage capacitor C1 (0.1 microfarad) charged by current drawn through to horn coil L and a resistor R7 (10 megohms). The time constant of resistor R5 and capacitor C1 controls the rate of charge of the capacitor C1 to the approximately 65 volt firing potential of a second neon glow discharge lamp Ne2 such that firing potential occurs about twice a second. Firing of the second neon lamp Ne2 discharges capacitor C1 through a resistor R5 1 kilohm) and applies a closing pulse of voltage to the gate 3 of the SCR switch Q2, drawing current through the horn coil L for one half-wave or less of the supply current. Then, because the reactive surge of the horns inductance L is shunted through the diode D5, the SCR switch opens and in succeeding rectified half-wave cycles the capacitor C1 recharges. The 2 cycle per second rate at which the pulsing circuit draws current through the horn causes the horn to click at the slow 2 c.p.s. rate. This slow rate is distinctly different from the 60 c.p.s. steady sound emitted when the horn continuously draws the half-wave rectified current.

The two distinctly different alarm indications are given by the same horn, with the elimination of the prior electromechanical indicator or alarm, and the addition only of inexpensive and reliable solid state components and a long life neon glow discharge device.

Shown in FIG. 2 is a smoke detector circuit similar to that of FIG. 1 but provided with an electronic relay circuit in lieu of the mechanical relay circuit of FIG. 1. Also added is a 22 megohm resistor in parallel with photocell PC2. Like numbered components are identical in FIGS. 1 and 2. The circuit of FIG. 2 actuates the pulsing circuit C], R5, R7, N62 if the lamp Dsi opens. A transistor ()3 is connected in parallel with the lamp by a coupling resistor R8 (47 kilohms) and is normally held conducting with lamp current through a resistor R4 (270 ohms) coupled by a resistor R9 (2.7 kilohms) to its base. If the lamp DSl opens transistor Q3 ceases conducting and allows a capacitor C5 (2 microfarad) to charge to the peak voltage supplied by the transistor 01. Current through a zener diode D6 (lN753A), and resistors R (1 kilohm) and R7 then allows charging of the pulsing capacitor C1.

As in the circuit of FIG. 1, when the pulsing capacitor C1 reaches the firing voltage of neon lamp Ne2, the pulsing capacitor C1 discharges through resistor R5 gating the SCR Q2 closed and sounding the horn H at the previously described clicking rate.

The tendency of the horn inductance L to keep the SCR Q2 latched through a full cycle is accompanied by the tendency of the anode of diode D5 to become positive with respect tocapacitor C4. in this case the diode D5 conducts current through the resistor R10 whose voltage drop triggers a second SCR O4 to conduction allowing the SCR Q4 and the diode D5 to shunt the inductive surge of the horn coil L.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents falling within the scope of the appended claims.

I claim:

1. An electrical alarm instrument for sensing a physical condition comprising,

an electrical alarm,

a controlled switch in series with the alarm and having a control,

a single, common power supply connected to the alarm and switch,

a condition responsive circuit connected to the switch control to close the switch and actuate the alarm in a mode dependent on the power supply, and

pulsing means connected between the power supply and the switch control for pulse storage from said common power supply and discharge to the switch control thereby to close the switch and actuate the alarm in a different mode dependent on the pulsing means, I

the responsive circuit including coupling means connected between the condition responsive circuit and pulsing means responsive to failure in said circuit to render the pulsing means effective,

whereby the alarm indicates condition response and circuit failure differently.

2. An instrument according to claim 1 wherein said pulsing means comprises a resistor-and capacitor having a characteristic time constant.

3. An instrument according to claim 2 wherein said pulsing means comprises a breakdown device connecting said capacitor and switch control when the capacitor is charged to a predetermined voltage effective to open the switch.

4. An instrument according to claim 1 wherein said power supply cycles at a predetermined rate and said pulsing means stores and discharges at a distinctly different rate.

5. An instrument according to claim 4 wherein said pulsing means comprises a resistor and capacitor having a characteristic time constant.

6. An instrument according to claim 4 wherein said power supply comprises a half-wave rectifier.

7. An instrument according to claim 6 wherein said switch comprises a controlled rectifier tending to open on unrectified half cycles.

8. An instrument according to claim 7 wherein said alarm comprises an inductance reacting to each unrectified half cycle to maintain power through the controlled switch during unrectified half cycles.

9. An instrument according to claim 8 characterized by a unidirectional conducting device connected between the power supply and said capacitor, the switching means of said photo-responsive circuit being effective on circuit failure to connect said device in shunt with the alarm inductance and prevent the inductance from maintaining power through the controlled switch.

10. An instrument according toclaim 1 wherein said responsive circuit includes a photosensitive device and an exciter lamp therefor and said switching means comprises a relay in series with the lamp.

11. An instrument according to claim 10 wherein said relay actuates a contact connecting the power supply to the pulsing means upon circuit failure.

12. An instrument according to claim 11 wherein said alarm comprises an inductance reacting to each unrectified half cycle to maintain power through the controlled switch during unrectified half cycles, characterized by a unidirectional conducting device, said relay contact connecting said device in shunt with the alarm inductance upon circuit failure.

13. An instrument according to claim 10 wherein said photosensitive device comprises a photocell shielded from the exciter lamp and viewing an area illuminated by the lamp, whereby to respond to light scattered by fluid born particles in the illuminated area.

14. A smoke detector for operation on alternating current comprising,

a power supply having positive and negative busses,

a smoke sensing circuit,

an alarm circuit, and

a failure sub-circuit,

the power supply including a half-wave rectifier of the alternating current connected to the positive and negative busses, and voltage regulator means connected to the busses,

the smoke sensing circuit including an exciter lamp and a relay connected to the busses, and a photocell connected to the busses, the cell being shielded from the exciter lamp and viewing the area illuminated by the lamp;

the alarm circuit including an inductive signaling device in series with a controlled rectifier and connected to said busses, the gate of said controlled rectifier being connected to the photocell and responsive thereto to complete a circuit through the signalling device, and

the failure sub-circuit comprising a diode, a resistance and a capacitor in series between the busses, the resistance and capacitor having a time constant substantially greater than the current alterations, a gas discharge breakdown device to the junction of the resistance and capacitor and to the controlled rectifier gate, and the relay contact having a position connecting the inductive signalling device to the capacitor and connecting the diode in shunt with the inductive signalling device.

i '0' k i 

1. An electrical alarm instrument for sensing a physical condition comprising, an electrical alarm, a controlled switch in series with the alarm and having a control, a single, common power supply connected to the alarm and switch, a condition responsive circuit connected to the switch control to close the switch and actuate the alarm in a mode dependent on the power supply, and pulsing means connected between the power supply and the switch control for pulse storage from said common power supply and discharge to the switch control thereby to close the switch and actuate the alarm in a different mode dependent on the pulsing means, the responsive circuit including coupling means connected between the condition responsive circuit and pulsing means responsive to failure in said circuit to render the pulsing means effective, whereby the alarm indicates condition response and circuit failure differently.
 2. An instrument according to claim 1 wherein said pulsing means comprises a resistor and capacitor having a characteristic time constant.
 3. An instrument according to claim 2 wherein said pulsing means comprises a breakdown device connecting said capacitor and switch control when the capacitor is charged to a predetermined voltage effective to open the switch.
 4. An instrument according to claim 1 wherein said power supply cycles at a predetermined rate and said pulsing means stores and discharges at a distinctly different rate.
 5. An instrument according to claim 4 wherein said pulsing means comprises a resistor and capacitor having a characteristic time constant.
 6. An instrument according to claim 4 wherein said power supply comprises a half-wave rectifier.
 7. An instrument according to claim 6 wherein said switch comprises a controlled rectifier tending to open on unrectified half cycles.
 8. An instrument according to claim 7 wherein said alarm comprises an inductance reacting to each unrectified half cycle to maintain power through thE controlled switch during unrectified half cycles.
 9. An instrument according to claim 8 characterized by a unidirectional conducting device connected between the power supply and said capacitor, the switching means of said photo-responsive circuit being effective on circuit failure to connect said device in shunt with the alarm inductance and prevent the inductance from maintaining power through the controlled switch.
 10. An instrument according to claim 1 wherein said responsive circuit includes a photosensitive device and an exciter lamp therefor and said switching means comprises a relay in series with the lamp.
 11. An instrument according to claim 10 wherein said relay actuates a contact connecting the power supply to the pulsing means upon circuit failure.
 12. An instrument according to claim 11 wherein said alarm comprises an inductance reacting to each unrectified half cycle to maintain power through the controlled switch during unrectified half cycles, characterized by a unidirectional conducting device, said relay contact connecting said device in shunt with the alarm inductance upon circuit failure.
 13. An instrument according to claim 10 wherein said photosensitive device comprises a photocell shielded from the exciter lamp and viewing an area illuminated by the lamp, whereby to respond to light scattered by fluid born particles in the illuminated area.
 14. A smoke detector for operation on alternating current comprising, a power supply having positive and negative busses, a smoke sensing circuit, an alarm circuit, and a failure sub-circuit, the power supply including a half-wave rectifier of the alternating current connected to the positive and negative busses, and voltage regulator means connected to the busses, the smoke sensing circuit including an exciter lamp and a relay connected to the busses, and a photocell connected to the busses, the cell being shielded from the exciter lamp and viewing the area illuminated by the lamp; the alarm circuit including an inductive signaling device in series with a controlled rectifier and connected to said busses, the gate of said controlled rectifier being connected to the photocell and responsive thereto to complete a circuit through the signalling device, and the failure sub-circuit comprising a diode, a resistance and a capacitor in series between the busses, the resistance and capacitor having a time constant substantially greater than the current alterations, a gas discharge breakdown device to the junction of the resistance and capacitor and to the controlled rectifier gate, and the relay contact having a position connecting the inductive signalling device to the capacitor and connecting the diode in shunt with the inductive signalling device. 